In a conventional magnetic storage system, a thin film magnetic head includes an inductive read/write element mounted on a slider. The magnetic head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
In the current magnetic storage technology, thin film, inductive write heads typically fall under two categories: longitudinal recording heads and perpendicular recording heads. Until recently, longitudinal recording heads have preceded perpendicular recording heads. As the continual push for very high density storage media has been the established trend in this field of technology, perpendicular recording heads have gained increasing acceptance owing to the ability of the perpendicular recording heads to provide more efficient recording methods for high-density storage applications than the longitudinal recording heads.
A perpendicular recording head is functionally distinguishable from a longitudinal recording head in the direction of the magnetic flux orientation with respect to the media such as a magnetic disk. During a write operation to a target track, the perpendicular recording head directs the magnetic flux substantially normal to the surface of the magnetic disk. This normal orientation is also the anisotropy direction of the media. In contrast, the magnetic flux developed by the longitudinal recording head is generally in the plane of the surface of the magnetic disk.
Further exemplary differences in the features of the two types of thin film, inductive write heads can be summarized as follows:
Longitudinal write heads typically employ a ring head configuration that is comprised of two magnetic poles separated by a narrow gap in between, to optimize the magnetic field in the longitudinal direction. Referring to FIG. 3 (FIGS. 3A, 3B), an exemplary longitudinal write head typically includes a thin film write head with a bottom pole (P1) and a top pole (P2).
The pole P1 has a pole tip height dimension commonly referred to as “throat height”. In a finished write head, the throat height is measured between an air bearing surface (“ABS”), formed by lapping and polishing the pole tip, and a zero throat level where the pole tip of the write head transitions to a back region. The pole tip region is defined as the region between the ABS and the zero throat level. This region is also known as a pedestal, which is an extension of the pole P1.
Similarly, the pole P2 has a pole tip height dimension commonly referred to as “nose length”. In a finished write head, the nose is defined as the region of the pole P2 between the ABS and the “flare position” where the pole tip transitions to a back region.
Each of the poles P1 and P2 has a pole tip located in the pole tip region. The tip regions of the poles P1 and P2 are separated by a magnetic recording gap, which is a thin layer of insulation material. During a write operation, the magnetic field generated by the pole P1, channels the magnetic flux from the pole P1 to the pole P2 through an intermediary magnetic disk, thereby causing the digital data to be recorded onto the magnetic disk.
The magnetic flux immediately originated from the pole P1 and directed towards the pole P2 is substantially parallel with respect to the surface of the magnetic disk. This portion of the magnetic field is typically considered as a fringe field, which is responsible for the write operation of a longitudinal write head.
In the current magnetic storage technology, longitudinal magnetic recording is considered to have reached a thermal stability limit beyond which no significant increase in the areal density of magnetic media for use with longitudinal write heads could be achieved. This is due to the reduced thickness of the magnetic media in order to achieve reduced transition width as necessitated by the increase in the areal density. The transition width is the distance over which the magnetization of the stored bits changes.
In addition, since the signal-to-noise ratio is proportional to the number of grains in the bit volume, the grain size needs to be reduced as the bit volume becomes smaller. This poses a severe problem of thermal instability for the magnetization of the magnetic grain.
To address the aforementioned problems and the continual technological push for higher density magnetic storage devices, perpendicular write heads have become increasingly desirable. Specifically, the demagnetization field in a perpendicularly written bit tends to enhance the stability of neighboring bits. As a result, narrower transitions can be recorded in the perpendicular recording mode. The magnetic media used with perpendicular recording heads can be made thicker, and thus can have higher thermal stability than those used with longitudinal recording heads. The use of a soft underlayer can enhance the perpendicular or normal component of the magnetic field and field gradient generated by the perpendicular write head.
To accomplish this objective, the soft underlayer, which is deposited beneath a recording layer, is made of a high moment magnetic material. During a write operation, any magnetic flux approaching the soft underlayer from the write pole in effect creates a virtual image of the write pole, thereby enabling a much higher magnetic write field and sharper field gradient.
Practically, perpendicular write heads could be constructed by appropriate modification of conventional longitudinal write heads. Using this derivative technology, an exemplary perpendicular write head may still use a ring head configuration of a conventional longitudinal write head with two magnetic poles, similarly referred to as P1 and P2.
Referring to FIG. 4, a significant feature of a perpendicular write head that substantially departs from a conventional longitudinal write head, is the large distance between poles P1 and P2. A narrow gap between poles P1 and P2 is essential in longitudinal write heads but are not needed in perpendicular write heads. This is so because the most optimal configuration of a perpendicular write head usually is a single pole design.
Thus, in the exemplary perpendicular write head of FIG. 4, the pole P2 would be considered as the write pole responsible for generating the magnetic flux in the perpendicular direction during a write operation. The magnetic flux permeates into the magnetic medium for use with perpendicular write heads to enable a recording of digital data onto the magnetic disk. The pole P1 provides a return path for the magnetic flux.
The continual demand for a high areal density design of magnetic storage media has necessitated a reduction in the track width as a means to increase the track density without significantly altering the geometry of the storage medium. As the track width is reduced, a significant concern with a conventional perpendicular write head design arises.
Referring now to FIG. 5, the pole tip 109 (shown in dotted line) of the pole P2 of a conventional perpendicular write head typically is of a rectangular shape (or footprint) that is defined by a width and a thickness, as viewed from the air bearing surface (ABS). The width of the pole P2 tip is referred to as the track width, and the thickness of the pole P2 tip is typically much greater than the track width.
During a write operation, the pole P2 tip imposes onto a target data track of the magnetic disk a magnetically active area of the size of the physical area of the pole P2 tip. Because the data tracks are generally concentric, but the pole P2 tip is rectangular, only a part of the magnetically active area is properly focused onto the target track, while the remaining magnetically active area is actually focused (i.e., skewed) onto the adjacent tracks, thereby causing a disturbance of the previously recorded bit.
This phenomenon is also referred to as side-writing. The side-writing action may, in a worst case scenario, result in an accidental, complete erasure of data in these adjacent tracks. Thus, without data verification and correction in between each write operation, the data quality of a magnetic disk could be significantly compromised.
Still, another significant concern with a conventional perpendicular write head design lies in the less than optimal performance of the write pole P2 due to the material characteristics of the pole P2. In a conventional perpendicular write head, the pole P2 is made of conventional electroplated magnetic materials such as NiFe or CoNiFe in accordance with the longitudinal write head technology from which conventional perpendicular write head design is derived.
While the conventional electroplated magnetic material is sufficient in longitudinal write head design utilizing two write poles, it is deemed inadequate for a single write pole design in conventional perpendicular write heads. Because of the single write pole design, the conventional magnetic material does not demonstrate sufficiently high degrees of magnetic moment, permeability, and other desirable properties to generate enough magnetic field strength to achieve an optimal data recording.
Thus, in light of the foregoing problems, there is still an unsatisfied need for a technologically more efficient design of perpendicular write heads. This design should resolve the long standing issue of data erasure in adjacent tracks due to side-writing, while also addressing the need for enhancing the magnetic write field strength without compromising the manufacturability of perpendicular write heads.